makepromise

makepromise

Make native Promise from function with callback

makePromise(fn:Function(...args, cb:Function(err:Error, res:any))) => Promise<any>

Create a promise from a function which accepts callback as the last argument, and where callback will be called with (error, result).

For example, you can unlink a closed file:

'use strict'

const fs = require('fs')
const wrote = require('wrote')
const makePromise = require('makepromise')

let file
wrote() // create a temp file and open a writable stream
    .then((ws) => {
        file = ws.path
        console.log(ws.path) // /var/folders/s0/tmp/T/wrote-69822.data
        return new Promise((resolve, reject) => {
            ws.once('close', resolve)
            ws.once('error', reject)
            ws.close()
        })
    })
    .then(() => {
        const promise = makePromise(fs.unlink, file)
        return promise
    })
    .then(
        console.log, // undefined
        console.error
    )

makePromise(fn:Function(...args, cb:Function(err:Error, res:any), resolveValue:any)) => Promise<any>

Pass resolveValue as second argument to make promise be resolved with it.

'use strict'

const fs = require('fs')
const wrote = require('wrote')
const makePromise = require('makepromise')

let file
wrote() // create a temp file and open a writable stream
    .then((ws) => {
        file = ws.path
        console.log(ws.path) // /var/folders/s0/tmp/T/wrote-69822.data
        return new Promise((resolve, reject) => {
            ws.once('close', resolve)
            ws.once('error', reject)
            ws.close()
        })
    })
    .then(() => {
        const promise = makePromise(fs.unlink, file, file)
        return promise
    })
    .then(
        (res) => { console.log(res === file) }, // true
        console.error
    )

More examples

Check test/spec/integration for the following tests:

• How to unlock a file with lockfile and close write stream
• How to write to a file stream open with fs.createWriteStream() and end the stream
• How to unlink a file with fs.unlink
• How to read stat with fs.stat
• How to catch errors (example with trying to call fs.stat with non-existent file)

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Licence: MIT

(c) Sobesednik-Media 2017